From: Li Zefan <lizf@cn.fujitsu.com>
To: Johannes Berg <johannes@sipsolutions.net>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@elte.hu>,
Frederic Weisbecker <fweisbec@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>
Subject: Re: event tracing, ringbuffer and RB_MAX_SMALL_DATA
Date: Wed, 15 Jul 2009 09:08:06 +0800 [thread overview]
Message-ID: <4A5D2BF6.6010802@cn.fujitsu.com> (raw)
In-Reply-To: <1247591891.7178.20.camel@johannes.local>
Johannes Berg wrote:
> Hi,
>
> By code inspection, I think there's a bug if your event contains only
>
> __dynamic_array(u8, buf, buflen)
>
> and your buflen is only, say, 3. Then the event size will be the common
> event size (12 bytes) plus this, so 15, which is well below
> RB_MAX_SMALL_DATA (4*28 = 112), so it'll be divided by four to be stored
> into type_len. At this point, however, you've lost the information that
> your dynamic array was only three bytes, and it'll be considered _four_
> bytes long by parsers as far as I can tell?
>
Right, the length of a dynamic array is not recorded, and this
causes 2 problems:
- the event filter is not working properly for dynamic strings
- userspace parsers can't figure out the length of those arrays
I had an idea some time ago, and hopefully will send out a
patch today or tomorrow.
next prev parent reply other threads:[~2009-07-15 1:09 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-07-14 17:18 event tracing, ringbuffer and RB_MAX_SMALL_DATA Johannes Berg
2009-07-15 1:08 ` Li Zefan [this message]
2009-07-15 9:48 ` Johannes Berg
2009-07-16 0:48 ` Li Zefan
2009-07-21 1:25 ` Steven Rostedt
2009-07-21 1:30 ` Li Zefan
2009-07-21 1:42 ` Steven Rostedt
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=4A5D2BF6.6010802@cn.fujitsu.com \
--to=lizf@cn.fujitsu.com \
--cc=fweisbec@gmail.com \
--cc=johannes@sipsolutions.net \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@elte.hu \
--cc=rostedt@goodmis.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.